\documentclass{standalone}    
\usepackage{pgf}
\usepackage{tikz}
\usepackage{stix}
\usetikzlibrary{arrows,automata,positioning}
\begin{document}
\usetikzlibrary{arrows.meta}
\begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=2.8cm]
    \tikzstyle{every state}=[fill=white,draw=black]
    \node[state] (A) at (0,0) {-1};
    \node[state] (B) at (2,0) {0};
    \node[state] (C) at (4,0) {1};
    \node[state] (D) at (6,0) {$\sqrt{2}$};
    \begin{scope}[>={Stealth[black]},
        every edge/.style={draw=black, semithick}]
        \path 
            (A) edge [loop below] node {$\leq$} (A)
                edge node {$\leq$}  (B)
                edge [bend left]  node {$\leq$}  (C)
                edge [bend left]  node {$\leq$}  (D)
            (B) edge [loop below] node {$\leq$} (B)
                edge node {$\leq$} (C)
                edge [bend left]  node {$\leq$}  (D)
            (C) edge [loop below] node {$\leq$} (C)
                edge node {$\leq$}  (D)
            (D) edge [loop below] node {$\leq$} (D);

    \end{scope}
\end{tikzpicture}  
\end{document}